Had a similar experience with a M38 Swedish Mauser… I used folded-over black electrical tape in the barrel channel. Worked well enough that when I changed stocks to a Fajen, I built a similar pad from barrel bedding material. I shimmed the stock a millimeter or so at the front action screw, put in the barrel bedding, and let it all set up. When dry I removed the shim from the front action screw and tightened it down – had a nice permanent shim putting upward pressure at the end of the stock.

I will give this a try. I have long suspected electrical tape, but Cork makes more sense. The Finns used thin pieces of Brass. I have also heard about shimming the barrel at the places where the outer bands are attached. That would POSSIBLY make sense: Increasing pressure, in order to dampen vibrations. Everything that we know about Physics, tells us that we need to DAMPEN vibrations — not ALLOW vibrations. I suspect that such is the reason why some Mosin-Nagant rifles are more accurate when fired with the Bayonet affixed. The problem is that there is no substitute for trial and error. The Military Surplus Russian rifles are notorious for inconsistency from one rifle to another of the same model. That is part of the reason for free-floating. For example, a given rifle may not be exactly chambered in the very center of the barrel. Hence, free-floating will not accentuate asymmetrical vibrations like shimming could. I will experiment with 4 rifles. At some future date, I will have results to post. Everybody complains about Mosin-Nagant triggers. That is not in dispute. I like cheap solutions.